Renewal/Registration System
In order for the OpenBubbles to operate, it needs to stay registered with iMessage. OpenBubbles does this with your device's hardware identifiers (serial number, board ID, model, etc.) by sending them to Apple for validation. OpenBubbles refers to this info in the app as "hardware info".
OpenBubbles needs to renew periodically to stay registered with iMessage. Go to Settings -> Your Profile -> iMessage status to see the next scheduled renew.
Mac
OpenBubbles and register and renew indefinitely with no connection to the Mac.
iPhone
Maintaining registrtation requires the iPhone and relay to stay online. Apple can force a re-registeration at any time, therefore your iPhone must be online at all times.
Your profile page shows the next scheduled re-registration.
How to deregister
Deregister if you no longer want Apple users to message you on iMessage.
Reset the App in Settings -> Reset. Then, visit https://account.apple.com/ and delete the device that was used with OpenBubbles.
If you have already uninstalled and registered your number, visit https://selfsolve.apple.com/deregister-imessage/ to deregister your number.